In recent years, the extent of integration of semiconductor components has been continually increasing. The resolution capacity that can be obtained with conventional deep-UV microlithography has thus appeared to reach its limits. Normally, it is not generally possible to produce, on a substrate, conventional structures with dimensions of less than 0.25 .mu.m, as is required for the production of particularly highly integrated electronics components. These components generally have minimal dimensions down to approximately 0.12 .mu.m. In order to be able to resolve sufficiently, in an optical manner, such fine structural elements, particularly short-wave radiation must be utilized, which generally has a wavelength between 190 and 260 nm.
However, present conventional G-line, I-line and deep-UV (DUV) photoresistant materials are poorly suited for radiation of such wavelength. These conventional materials are usually based on phenolic resins as binders, for example, on novolak resins or on chemically amplified polyhydroxystyrene derivatives with acid labile groups, which show a strong absorption at wavelengths below 260 nm. This leads to the fact that, with the use of such radiation, the side walls of the finished developed resist structures do not form the targeted right angle, but rather form a more or less oblique angle with the substrate or the resist surface, which nullifies the obtaining of optical resolution as a consequence of the use of shortwave radiation.
Photoresists without a sufficiently high proportion of aromatic components, e.g., resists based on methacrylate resins, have proven sufficiently transparent for radiation below 260 nm, but they do not have the plasma etch resistance that is customary for resists based on aromatic resins; plasma etching being one principal method for producing microstructures on silicon substrates. The plasma etch resistance, as is known, is essentially based on the aromatic groups in these resists.
ArF excimer base (193 nm) lithography is a prime candidate for sub 0.18 .mu.m lithography. The leading resist technology approaches for practical 193 nm lithography are top surface imaging (TSI) bilayer resists and single layer. Each approach has its own characteristic advantages and disadvantages as the result of the underlying technology and the materials, which can be utilized. The numerous problems for the 193 nm photoresist chemists to solve, (e.g., transparency, photospeed, adhesion, sensitivity, various process time delay latitudes, and plasma etch resistance), are somewhat different for each technology due to the materials requirements.
Lithographic aspect ratios and other issues require that resist films be thinner (about 0.5 .mu.m) for sub 0.18 .mu.m devices. This, in turn, requires either greatly improved etch processes or improved etch resistance or both. Thus, having excellent plasma etch resistance is critical and it is preferable that it be even better than before because of the thinner films. This presents a materials problem to the resist chemist because now both the aromatic character and the alkali-solubilizing group must be replaced. Thus, new materials, or groups of materials, with high transparency, etch resistance, and a different alkali-solubilizing group are required.
Single layer resists based on alicyclic polymers, for example, based on cyclic hydrocarbons such as norborene, have been found to be transparent enough at 193 nm and to have reasonable plasma etch resistance. However, the alicyclic resins in their "pure state" suffer from high hydrophobicity and adhesion problems. Modifications to improve these and other properties tend to decrease the plasma etch resistance significantly below that of novolac based resins and offer little hope of improved etch resistance.
There have been various solutions proposed for this problem. One solution is offered by the use of a special multilayer technique, generally referred to as bilayer resists. First, an initial resin coating, commonly called an undercoat layer, which is not photoimageable, is introduced onto the substrate. This undercoat layer provides the plasma etch resistance when etching the substrate. A second covering coating layer that can be photoimaged, which contains an organosilicon component instead of a component with a high content of aromatic compounds, is introduced onto the first planarizing layer. The substrate coated in this way is selectively exposed, i.e., in an image-forming way, in the conventional manner and then treated with a suitable developer, so that a desired image-forming structure is generated in the covering coating that can be photostructured. A subsequently conducted treatment in oxygen plasma leads to the organosilicon compounds being oxidized to silicon oxides, at least on the surface, and these oxides form a closed etching barrier or protective surface over the unexposed areas, for the oxidative decomposition of the organic material that lies underneath, particularly the planarizing layer, while the planarizing layer is removed completely in an oxidative manner on those places that are not coated by the silicon-containing covering layer.
Such bilayer resists generally offer improved depth of focus, resolution, substrate compatibility, and aspect ratios.
While various polymers have been proposed for use in such photoimageable top layer compositions in a bilayer system for photolithography at 193 nm wavelength radiation there is still a need for improved polymers with improved lithographic properties for this purpose, and especially for a bilayer system to provide high resolution deep UV lithography, particularly at 193 nm radiation.